[PATCH v7 5/6] compositor-fbdev: detect the first fb device in the seat

[Emil Velikov]

On 27 June 2018 at 00:39, nerdopolis <bluescreen_avenger at verizon.net> wrote:
> This adds a function to detect the first framebuffer device in the
> current seat. Instead of hardcoding /dev/fb0, detect the device
> with udev, favoring the boot_vga device, and falling back to the
> first framebuffer device in the seat if there is none. This is very
> similar to what compositor-drm does to find display devices
> ---
>  libweston/compositor-fbdev.c | 83 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 80 insertions(+), 3 deletions(-)
>
> diff --git a/libweston/compositor-fbdev.c b/libweston/compositor-fbdev.c
> index e3777495..616300dc 100644
> --- a/libweston/compositor-fbdev.c
> +++ b/libweston/compositor-fbdev.c
> @@ -777,6 +777,77 @@ session_notify(struct wl_listener *listener, void *data)
>         }
>  }
>
> +static char *
> +find_framebuffer_device(struct fbdev_backend *b, const char *seat)
> +{
> +       struct udev_enumerate *e;
> +       struct udev_list_entry *entry;
> +       const char *path, *device_seat, *id, *fb_device_path;
> +       struct udev_device *device, *fb_device, *pci;
> +
> +       e = udev_enumerate_new(b->udev);
> +       udev_enumerate_add_match_subsystem(e, "graphics");
> +       udev_enumerate_add_match_sysname(e, "fb[0-9]*");
> +
> +       udev_enumerate_scan_devices(e);
> +       fb_device = NULL;
> +       udev_list_entry_foreach(entry, udev_enumerate_get_list_entry(e)) {
> +               bool is_boot_vga = false;
> +
> +               path = udev_list_entry_get_name(entry);
> +               device = udev_device_new_from_syspath(b->udev, path);
> +               if (!device)
> +                       continue;
> +               device_seat = udev_device_get_property_value(device, "ID_SEAT");
> +               if (!device_seat)
> +                       device_seat = default_seat;
> +               if (strcmp(device_seat, seat)) {
> +                       udev_device_unref(device);
> +                       continue;
> +               }
> +
> +               pci = udev_device_get_parent_with_subsystem_devtype(device,
> +                                                               "pci", NULL);
> +               if (pci) {
> +                       id = udev_device_get_sysattr_value(pci, "boot_vga");
> +                       if (id && !strcmp(id, "1"))
> +                               is_boot_vga = true;
> +               }
> +
> +               /* If a framebuffer device was found, and this device isn't
> +                * the boot-VGA device, don't use it. */
> +               if (!is_boot_vga && fb_device) {
> +                       udev_device_unref(device);
> +                       continue;
> +               }
> +
> +               /* There can only be one boot_vga device. Try to use it
> +                * at all costs. */
> +               if (is_boot_vga) {
> +                       if (fb_device)
> +                               udev_device_unref(fb_device);
> +                       fb_device = device;
> +                       break;
> +               }
> +
> +               /* Per the (!is_boot_vga && fb_device) test above, only
> +                * trump existing saved devices with boot-VGA devices, so if
> +                * the test ends up here, this must be the first device seen. */
> +               assert(!fb_device);
> +               fb_device = device;
> +       }
> +
> +       udev_enumerate_unref(e);
> +
This function (barring the if bellow) seems mostly identical to the
one in compositor-drm.c
Might be a good idea to make it a helper vaguely alike

struct udev_device *
foo(struct backend *b, const char *seat, const char *subsys, const
char *sysname,
      int (*predicate)(struct backend b*, struct udev_device *d))

The callers will be as trivial as
foo(b, seat, "drm", "card[0-9]*", drm_device_is_kms);
foo(b, seat, "graphics", "fb[0-9]*", NULL);

You'd want to do this at some point, since close to nobody tests
fbdev. I think that people porting any drm fixes to fbdev is even less
;-)

> +       if (fb_device)
> +       {
> +               fb_device_path=strdup(udev_device_get_devnode(fb_device));
> +               udev_device_unref(fb_device);
> +       }
> +
Obviously this trivial hunk will have to stay in fbdev.

HTH
Emil